Candy from a Stranger by Daryl Buckner

What would you do if your child went missing and the police were ineffective? Exactly. You would start investigations yourself. When eight-year-old Lucas Cain is snatched, his father, Ben, dedicates his life to finding out what happened to his only child. His desperation leads to his life being torn to shreds: his marriage in tatters, his job lost and even his mind is altered. They all believe Ben has gone insane. Has he? Self-fulfilling prophecy kicks in as Ben starts to believe he may well have had a role in the disappearance. The police close in on him just as he is about to uncover the complex mystery.